The CDC, analyzing data from 2003 to 2010, found that the prevalence of hypertension among adults during that period was 30.4 percent, or almost 67 million Americans. Of the 53.5 percent who were not controlling their blood pressure, 39 percent did not know they had hypertension, 16 percent knew but took nothing to lower it, and 45 percent were taking medications to no avail.